1. Field of the Invention
The present invention relates to a pressure actuated sensor which serves as a switching device, for example, for activating and/or shutting down of equipment or machinery.
2. Background of the Art
Pressure actuated switches are known in the art. Such switches are used for example as safety mats, sensitive door edges, and the like. Typically, such switches include two spaced apart conductors. When pressure is applied the conductors contact each other, thereby closing an electrical circuit. This switching action can be used to activate or, alternatively, deactivate machinery. For example, on mechanically operated doors, the doors commonly include a sensitive edge switch. Should the edge switch make contact with an object in its path (e.g. a person) while the door is closing the edge switch will send a signal to a control unit to reverse or stop the movement of the door. Such edge switches may commonly be found on garage doors, train doors, and the like.
For example, U.S. Pat. No. 5,072,079 to Miller discloses a sensing edge causing a closing door to open by actuating a device upon force being applied to the sensing edge. The sensing edge includes a first sheet of resiliently compressible material, a first sheet of electrically conductive material, a layer of non-conductive material, a second sheet of electrically conductive material, a second sheet of resiliently compressible material and an elongate inner core arranged in the recited order. The inner core has a predetermined elastic compressibility which is selected in accordance with the desired sensitivity of the sensing edge, such that the sensitivity of the sensing edge directly corresponds to the elastic compressibility of the inner core. The first and second sheets of flexible, electrically conductive material are spaced apart by the layer of non-conductive material and present opposed portions to each other through an opening in the layer of non-conductive material whereby upon the application of force to the sheath, the inner core compresses until its elastic compressibility is less than the elastic compressibility of said first and second layers of resiliently compressible material and said layer of non-conductive material, whereupon a portion of the first sheet of flexible, electrically conductive material deflects into the opening in the second layer of non-conductive material and into contact with a portion of the second sheet of flexible, electrically conductive material to thereby actuate the device.
Other edge switches are disclosed, for example, in U.S. Pat. Nos. 5,027,552; 5,023,411; 4,920,241; 4,908,483; 4,785,143; 4,349,710; 4,273,974; 4,051,336; and 3,315,050.
While prior known edge switches are useful for detecting the presence of an object in the path of a moving door, being fully on or completely off they do not discriminate between the signals resulting from contact of the edge switch with large objects, and spurious signals resulting from, for example, disparities in the interfacing surfaces of the switch caused by uneven extrusion.